Liquefied gas as a fuel of prime movers in marine vessels and other mobile power plants has increasingly become of interest while importance of environmental issues of such as exhaust emissions have increased.
EP 2032428 B1 discloses an example of a fuel system for gas driven piston engine in a marine vessel, in which gas is stored in at least one fuel storage tank in the vessel as liquefied gas. The fuel feeding system includes a separate fuel feed tank in which the gas is in liquid phase and at elevated pressure. The gas is also in liquid phase in the fuel storage tank, in which, however, prevails only the hydrostatic pressure caused by the liquid gas.
As can be found from the document above liquefied gas can be stored at extremely low temperature and due to, for example, heat transfer from surrounding a part of the gas is evaporated as so called boil off gas.
The gas driven gas consumers configured to combust gaseous fuel have practically always some demands in respect to the pressure of the gas introduced to the gas consumer. Therefore the pressure is controlled.
For example in EP 2032428 B1 there is shown a pressure build up system which controls the pressure in the tank by controlling the evaporation of the liquefied gas in a heat exchanger of the pressure build up system. The fuel is taken from the bottom part of the tank as liquid fuel and the fuel in evaporated into gas before feeding to the engines.
WO2016163666 A1 discloses is a fuel gas supply system. The fuel gas supply system includes a storage tank for storing liquefied gas and boil-off gas of the liquefied gas; a compression unit for compressing the boil-off gas supplied from the storage tank; a first pump for pressurizing the liquefied gas supplied from the storage tank; a vaporizer for vaporizing the pressurized liquefied gas; a first supply line for supplying to an engine the boil-off gas, stored in the storage tank, via the compression unit; a second supply line for joining the boil-off gas, stored in the storage tank, at the rear end of the compression unit of the first supply line, via the first pump and the vaporizer; a measurement unit for measuring the pressure or amount of the boil-off gas supplied to the engine; and a control unit for controlling the first pump and the vaporizer on the basis of the measured value, and supplying the liquefied gas through the second supply line.
The foregoing documents and their disclosures are incorporated herein by reference in their entireties.